Field of the Invention
Embodiments of the invention generally relate to a plasma processing chamber having a RF return path with low impedance and the method for using the same.
Description of the Related Art
Liquid crystal displays (LCDs) or flat panels are commonly used for active matrix displays such as computers, touch panel devices, personal digital assistances (PDAs), cell phones, television monitors, and the like. Further, organic light emitting diodes (OLEDs) have also been widely used for flat panel displays. Generally, flat panels comprise two plates having a layer of liquid crystal material sandwiched therebetween. At least one of the plates includes at least one conductive film disposed thereon that is coupled to a power source. Power, supplied to the conductive film from the power supply, changes the orientation of the crystal material, creating a patterned display.
In order to manufacture these displays, a substrate, such as a glass or polymer workpiece, is typically subjected to a plurality of sequential processes to create devices, conductors and insulators on the substrate. Each of these processes is generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, a number of process chambers are typically coupled to a transfer chamber that houses a robot to facilitate transfer of the substrate between the process chambers. One example of a processing platform having this configuration is generally known as a cluster tool, examples of which are the families of plasma enhanced chemical vapor deposition (PECVD) processing platforms available from AKT, a division of Applied Materials, Inc., of Santa Clara, Calif.
As demand for flat panels has increased, so has the demand for larger sized substrates. For example, large area substrates utilized for flat panel fabrication have increased in area from 550 mm by 650 mm to over 4 square meters in just a few years and are envisioned to continue to increase in size in the near future. This growth in the size of the large area substrates has presented new challenges in handling and production. For example, the larger surface area of the substrates requires increased grounding capacity of the substrate supports.
On conventional PECVD systems, a plurality of flexible conductive straps provides a ground path between the substrate support and chamber body. The grounding straps prevent RF arcing at the side of the substrate support, thereby preventing a secondary plasma from forming at the sides of the substrate support. Grounding straps are generally fabricated from aluminum sheets with a top portion of the grounding strap connected to the substrate support, and a bottom portion of the grounding strap connected to a chamber body wall. As the substrate support moves up and down, coupled with high processing temperatures (e.g., greater than 300 degrees Celsius), the aluminum grounding straps weaken due to thermal stress and eventually break. Since the grounding straps are not readily visible from the exterior of the processing chamber, operators are often unaware if the grounding straps are broken unless they stop processing and perform a visual inspection with a light source or physically open the processing chamber. Broken grounding straps may adversely affect the RF ground return path in the processing chamber, which results in defects and non-uniformity on the substrate.
Therefore, there is a need for an improved method of detecting grounding strap breakage without stopping processing or having to open the processing chamber.